Rolling bearing unit with rotation speed detection instrument for use in cars and method for working outer race for use in this bearing unit

ABSTRACT

A rolling bearing unit with a rotation speed detection instrument having a hub with a plurality of inner race tracks, an outer race formed of steel material with a plurality of outer race tracks, rolling elements between the tracks, and encoder on the hub and a sensor supported in a mounting hole in the cuter race. A hardened layer is formed on the inner surface of the outer race and each portion where the outer race tracks are formed. An area of the inner surface around the mounting hole is not hardened.

This application claims the benefits of Japanese Application Nos.10-54576, 10-57102 and 10-127725 which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rolling bearing unit with a rotationspeed detection instrument for use in cars, and to a method for workingan outer race for use in the bearing unit.

Particularly, the present invention relates to improvements in a rollingbearing unit with a rotation speed detection instrument which allows awheel of a car to be supported ratatably on a suspension device thereofand which is used to detect a rotation speed of the wheel, as well as toan outer race constituting the rolling bearing unit with the rotationspeed detection instrument.

2. Related Background Art

For rotatably supporting a wheel of a car onto a suspension device, arolling bearing unit is used. The rotation speed of the wheel must bedetected to control an antilock braking system (ABS) as well as atraction control system (TCS). For this reason, it has been widelyperformed that the foregoing wheel is rotatably supported onto thesuspension device by a rolling bearing unit with a rotation speeddetection instrument which is built therein and the rotation speed isdetected.

Such rolling bearing unit with a rotation speed detection instrumentsupports a hub on the inner diameter side of its outer race rotatablyinterposing a plurality of rolling elements between the outer race andthe hub.

At the same time, the rotation speed of an encoder fixed to a portion ofthe hub is detected by a sensor which is supported by a portion of theouter race. The characteristic of the encoder in the circumferencedirection is changed alternately at equal intervals. Moreover, thetechnology that the detection portion of the sensor is made to face theouter peripheral surface of a large diameter cylindrical portion of theencoder at a situation where the sensor is supported in a mounting holeformed at an intermediate portion of the outer race in its axialdirection and to be elongated in the diameter direction of the outerrace, has been widely known as disclosed in, for example, JapanesePatent Laid-open No. 63-59769, 6-109027, 8-210659, and manypublications.

When the roiling bearing unit with the rotation speed detectioninstrument as described above is used, the foregoing outer race issupported on the suspension device, the wheel is fixed to the endportion of the hub, which portion is located a part from the outer race,thereby the wheel being supported rotatably on the foregoing suspensiondevice. When the foregoing encoder rotates with the rotation of thewheel, the output of the sensor having the detection portion facing theencoder changes. The frequency in which the output of the sensor changesis proportional to the rotation speed of the wheel. Therefore, if theoutput signal of the sensor is sent to a controller which obtains therotation speed of the wheel, the ABS as well as the TCS can becontrolled suitably.

In the case of the rolling bearing unit with the rotation speeddetection device described in the foregoing gazettes, no considerationfor the compatibility of the workability of the mounting hole with asecurity of the durability of the outer race was made. Specifically, inorder to secure the rolling fatigue life time of the track or raceway ofthe outer race, a hardened layer having the hardness more than 500 Hvmust be formed in the inner peripheral surface of the enter race, and inthe surface of the outer race where the outer race tracks are formed andin the vicinity of that surface. This layer is formed to a depth (about1.5 mm in the case of the rolling bearing unit of cars) more than threetimes inclusive of three times as large as a depth where a shearingforce based on a stress applied by the rolling element becomes maximum(about 0.5 mm in the case of the rolling bearing unit of cars). Atransition layer of about 0.5 mm thick exists between the deepestportion of this hardened layer and its so-called raw portion which isnot hardened. In this transition layer portion, the hardness graduallydecreases from the hardened layer to the raw portion.

In order to form the hardened layer in each of the outer race trackportion, although the control of the hardening depth with respect to thethickness direction was considered, the regulation of the formationrange of the hardened layer in the surface direction of the innerperiphery of the outer race, particularly, in the axial direction, wasnot considered. Specifically, with respect to the thickness direction,in order to secure the toughness of the outer race, although to leavethe raw portion in the vicinity of the outer periphery of the outer racewas considered (see, for example, Utility Model Gazette No. 2529597),the consideration in the surface direction was not considered. Asdescribed above, when the thickness direction of the hardened layer isconsidered concerning the range of the hardened layer and the hardenedlayer is formed in each of the foregoing outer race track portionswithout considering the surface direction of the hardened layer, therange of the hardened layer may reach to about 10 mm from the endportion of each outer race track or more. The hardness of the hardenedlayer becomes high in the portion of about 10.5 mm or more apart fromthe end of each outer race track.

On the other hand, in response to the demand for saving fuel consumptionof the cars in recent years, to downsize the rolling bearing unit forsupporting the wheel and to reduce a weight of it, the shortening of thedimension of this rolling bearing unit in the axial direction has beendeveloped. Based on such shortening, the distance between the endperiphery of each cuter race track portion and the mounting hole becomesshort, and this distance sometimes can not be kept to be more than 10.5mm. For this reason, the hardness in the portion where the foregoingmounting hole is to be formed becomes high too, so that working of thismounting hole will be cumbersome. Although the working of this mountinghole may be well performed before the formation of the hardened layer ineach outer race track portion, when the hardened treatment is performedafter the working of the mounting hole, the considerations forpreventing the occurrence of defects due to stress concentration in themounting hole portion is needed, resulting in troublesomeness of thehardening treatment.

Furthermore, in Utility Model Gazette No. 2529597, the technology isdisclosed, in which the hardened layer is formed also in a portionbetween a plurality of the outer race tracks of the outer race in a partof the inner peripheral surface of the outer race, and the portionbetween the outer race tracks is made to be not liable to occur aplastic deformation. As described above, when the portion between theouter race tracks is made to be not liable to occur the plasticdeformation, the plastic deformation of the outer race is prevented, sothat an increase in durability of the rolling bearing unit with therotation speed detection instrument including this outer race can beachieved, in spite of the fact that an impact load is applied to theouter race due to crashing of the wheel to paving stones. It should benoted that even in such case, toughness of the outer race is securedwhile leaving a raw portion that is not hardened in the vicinity of theouter periphery of the outer race and occurrence of damages of the outerrace such as cracks due to the application of the foregoing impact loadcan be prevented.

However, when the hardened layer is formed also between the outer racetracks in the part of the inner peripheral surface of the outer race,working of the mounting hole to fixedly support the sensor, which isformed in the outer race, becomes difficult.

On the other hand, in response to the demand for saving fuel consumptionof the cars in recent years, to downsize the rolling bearing unit forsupporting the wheel and to reduce a weight of it, the shortening of thedimension of this rolling bearing unit in the axial direction has beendeveloped. Based on such shortening, the distance between the endperiphery of each outer race track portion and the mounting hole becomesshort, and this distance sometimes can not be kept to be more than 10.5mm. For this reason, the hardness in the portion where the foregoingmounting hole is to be formed becomes high too, so that working of thismounting hole will be cumbersome. Although working of this mounting holemay be well performed before the formation of the hardened layer in eachouter race track portion, when the hardening treatment is performedafter the working of the mounting hole, the considerations forpreventing the occurrence of defects due to stress concentration in themounting hole portion is needed, resulting in troublesomeness of thehardening treatment.

Furthermore, as described in the foregoing Utility Model Gazette No.2529597, the technology has been known, in which the hardened layer isformed also between a plurality of the tracks of the outer race in orderto enhance the durability of the rolling bearing unit with the rotationspeed detection instrument including the outer race by making the outerrace not liable to occur the plastic deformation, even when an impactload is applied to the outer race through the hub and the rollingelement owing to reasons such as crashing of the wheel against thepaving stone. As described above, in the case where the hardened layeris formed also between a plurality of the outer race tracks of the outerrace, the working of the foregoing mounting hole becomes cumbersome, notonly in the case of small-sized rolling bearing units but also even inthe case of comparatively large-sized rolling bearing unit with therotation speed detection instrument in which the distance between theend periphery of each outer race track portion formed in the innerperiphery surface of the outer race and the mounting hole, is relativelylarge.

SUMMARY OF THE INVENTION

From the viewpoint of the above described circumstances, the firstobject of the present invention is to provide a rolling bearing unitwith a rotation speed detection instrument which is capable ofperforming the working operation particularly for the foregoing mountinghole without making the hardening treatment troublesome.

The rolling bearing unit with a rotation speed detection instrument toachieve the first object comprises a hub rotating together with a wheelat the time of its use, the hub having a plurality of inner race tracksin an outer peripheral surface thereof; an outer race formed of steelmaterial, which at the time of its use, is supported stationary by asuspension device and does not rotates the outer race having a pluralityof outer race tracks in an inner peripheral surface to face the innerrace tracks; rolling elements, each being rotatably provided between theinner race track and the corresponding outer race track; an encoderfixedly fitted on a portion of the outer peripheral surface of the hubarid between the inner race tracks, the encoder exhibiting acharacteristic which changes in its circumference direction alternatelyat equal intervals; and a sensor having a detecting section, the sensorbeing supported in a mounting hole provided in an intermediate portionof the outer race in its axial direction to face the encoder andchanging its output signal in response to the change of thecharacteristic of the encoder, wherein a hardened layer is formed ineach outer race track portion in the inner peripheral surface of theouter race.

Particularly, the present invention is directed to the rolling bearingunit with the rotation speed detection instrument in which the distancebetween the mounting hole and an end periphery of the outer race trackclosest to the mounting hole among the plural outer race tracks is 10.5mm or less. In this rolling bearing unit with the rotation speeddetection instrument, the portion where the mounting hole is formed isnot hardened, and a hardened layer formed in the outer race trackclosest to the mounting hole has a thickness of 1.5 mm or more.

Furthermore, it is perferable that, in the rolling bearing unit with therotation speed detection instrument, the distance between the mountinghole and the end periphery of the outer race track closest to themounting hole among the outer race tracks is at a range from 2 to 10.5mm, and the minimum distance between the mounting hole and the hardenedlayer, which is formed in each outer race track portion and has ahardness of 500 Hv or more, is 0.5 mm or more.

In this case, a working operation for the mounting hole to mount orsupport the sensor in the outer race can be easily performed withoutdegrading the durability of each outer race track portion as well aswithout making a hardening treatment for each outer race track portiontroublesome. Specifically, since the mounting hole portion is notsubjected to hardening, the working of the mounting hole can be easilyperformed.

When the distance between the mounting hole and the end periphery of theouter race track close to this mounting hole is set to 2 mm or more, theminimum thickness of 1.5 mm for the hardened layer formed in each outerrace track portion, which is necessary for securing the durability ofeach outer race track, can be secured. Furthermore, by setting theminimum distance between the mounting hole and the hardened layer formedin each outer race track portion to 0.5 mm or more, the mounting holecan be formed in a raw material portion apart from a transition layer orat least in a semi-raw portion exhibiting a low hardness, and even afterthe hardened layer is formed in each outer race track portion, theworking of the mounting hole can be easily performed.

It is perferable that in the rolling bearing unit with the rotationspeed detection instrument to achieve the first object, the hardenedlayers provided in the portions where the outer race tracks are formedare connected by a jointing hardened layer provided at a position apartfrom the mounting hole in its circumference direction, which has ahardness of 500 Hv or more, and the minimum distance between thejointing hardened layer and the mounting hole is 0.5 mm or more.

According to the rolling bearing unit with the rotation speed detectioninstrument last described, even when an impact load is applied to theouter race through the hub and the rolling elements, the outer race doesnot tend to make a plastic deformation, and the working of the mountinghole can be in addition easily performed.

By virtue of the rotation bearing unit with the rotation speed detectioninstrument to achieve the first object, which is constructed asdescribed above, a wheel is supported rotatably on the suspensiondevice, and an operation to detect the rotation speed of the wheel isconducted similarly to that of the case of the conventional rotationbearing unit with a rotation speed detection instrument, which has beenwell known.

By the way, in the case of the rolling bearing unit with the rotationspeed detection instrument in which the hardened layer is formed also inthe position between the plural outer race tracks in the inner peripherysurface of the outer race, the working of the mounting hole formed inthe outer race to fixedly support the sensor becomes difficult.

Accordingly, the second object of the present invention is to provide aworking method of an outer race for use in a rolling bearing unit with arotation speed detection instrument which makes it possible to work asensor mounting hole even when a hardened layer is formed not only inthe portions where the outer race tracks are formed but also between aplurality ofthe outer race track portions in an inner peripheal surfaceof an outer race, an outer race obtained by this method, and a rollingbearing unit with a rotation speed detection instrument obtained by thismethod.

Furthermore, aiming at securing toughness of the outer race andpreventing occurrence of damages such as cracks in the outer raceregardless of an impact load which may be applied during running ofcars, in order to leave a raw portion which is not hardened by hardeningin the vicinity of an outer diameter side of the portion between theouter race tracks in a part of the outer race, a hardened layer must beformed in an inner peripheral surface of the outer race while cooling anouter peripheral surface of the outer race with coolant. A furtherobject of the present invention is to provide a working method which iscapable of preventing the occurrence of unevenness of the hardened layerdue to an invasion of the coolant into the inner peripheral surface ofthe outer race.

A rolling bearing unit with a rotation speed detection instrument toachieve the second object of the present invention comprises; a hubrotating together with a wheel at the time of its use, the hub having aplurality of inner race tracks in an outer peripheral surface thereof;an outer race which, at the time of its use, is supported stationary bya suspension device and does not rotates, the outer race having aplurality of outer race tracks in an inner peripheral surface of theouter race to face the inner race tracks; rolling elements, each beingrotatably provided between the inner race track and the correspondingouter race track; an encoder fixedly fitted on a portion of the outerperipheral surface of the hub between the inner race tracks, the encoderexhibiting a characteristic which changes in its circumference directionalternately at equal intervals; and a sensor having a detecting section,the sensor being supported in a mounting hole provided in anintermediate portion of the outer race in its axial direction in a statewhere the detecting section faces the encoder and changing its outputsignal in response to the change of the characteristic of the encoder,and wherein a hardened layer is formed in the portions where the outerrace tracks are formed and in the portion between the outer race tracks,in the inner peripheral surface of the outer race, and the mounting holeis formed using a drill having a super-hard drill or a ceramic chip,while cooling and lubricating a cut portion by cutting oil.

Furthermore, in a method for working the outer race constituting theforegoing rolling bearing unit with the rotation speed detectioninstrument is preferably performed in such manner that the hardenedlayer in the portions of the outer race where the plural outer racetracks are formed in the inner peripheral surface of the outer race anda portion between both the outer race tracks is formed, and thereafter amounting hole is formed in the intermediate of the outer race in theaxial direction thereof and between the plural outer race trackportions, using an ultrahard drill or a drill provided with a ceramicclip, while cooling and lubricating a cut portion by cutting oil.

In a method of working the outer race of the rolling bearing unit withthe rotation speed detection instrument, it is preferable that thehardened layer in the inner peripheral surface of the outer race and atthe portions where the outer race tracks are formed and at the portionbetween both the outer race tracks, is formed while cooling said outerrace from the outer periperal surface side by coolant, and a cuttingspeed of the drill for forming a mounting hole is 20 m/min. or lessexpressed by speed of an outer peripheral surface of the drill.

In the rolling bearing unit with the rotation speed detection instrumentto achieve the second object, in a situation where the mounting hole isformed from the outer peripheral surface side of the outer race to acertain portion in a diameter direction of the outer race, the hardenedlayer can be formed by heating the inner peripheral surface of the outerrace while cooling the outer race from its outer peripheral surface sideby coolant, and the mounting hole can be completed by perforatingthrough to the inner peripheral surface of the outer race after thehardened layer is formed.

In a method for working an outer race constituting the rolling bearingunit with the rotation speed detection instrument to achieve the secondobject, it is preferable that after the mounting hole is formed from theouter peripheral surface side of the outer race to a certain portion ina diameter direction of the outer race, the hardened layer is formed byheating the inner peripheral surface of the outer race while cooling theouter race from its outer peripheral surface side by coolant, and themounting hole is completed by perforating through to the innerperipheral surface of the outer race after the hardened layer is formed.

In the rolling bearing unit with the rotation speed detection instrumentto achieve the second object, after the mounting hole is formed, thehardened layer may be formed by heating the inner peripheral surface ofthe outer race while cooling the outer peripheral surface of the outerrace by coolant in a state where the mounting hole is hermeticallysealed or substantially sealed by a plug.

In a method for working the outer race constituting the rolling bearingunit with the rotation speed detection instrument to achieve the secondobject, after the mounting hole is formed at a portion between the outerrace tracks, in an intermediate portion of the outer race in its axialdirection, the hardened layer may be formed by heating the innerperipheral surface of the outer race while cooling the outer peripheralsurface of the outer race by coolant in a state where the mounting holeis hermetically sealed or substantially sealed by a plug.

In the rolling bearing unit with a rotation speed detection instrumentto achieve the second object, after the mounting hole is formed, thehardened layer may be formed by, while rotating the outer race, heatingthe inner peripheral surface of the outer race and cooling the outerperipheral surface of the outer race by coolant blown upward.

In a method for working the outer race constituting the rolling bearingunit with the rotation speed detection instrument to achieve the secondobject, after the mounting hole is formed in an intermediate portion ofthe outer race in its axial direction and at a portion between the outerrace tracks, the hardened layer may be formed by, while rotating theouter race, heating the inner peripheral surface of the outer race andcooling the outer peripheral surface of the outer race by coolant blownupward.

In the rolling bearing unit with the rotation speed detection instrumentto achieve the second object, after the mounting hole is formed, thehardened layer may be formed by heating the inner peripheral surface ofthe outer race while cooling the outer peripheral surface of the outerrace by gaseous coolant.

In a method for working the outer race constituting the rolling bearingunit with the rotation speed detection instrument, after the mountinghole is formed in an intermediate portion of the outer race in its axialdirection and at a portion between the outer race tracks, the hardenedlayer may be formed by heating the inner peripheral surface of the outerrace while cooling the outer peripheral surface of the outer race bygaseous coolant.

According to the bearing unit with the rotation speed detectioninstrument and the method for working the outer race for use in thebearing unit with the rotation speed detection instrument to achieve thesecond object, the mounting hole for fixedly supporting the sensor maybe formed even in the outer race provided with the hardened layer forpreventing deformation. Therefore, a bearing unit with a rotation speeddetection instrument which comprises an outer race which is not apt todeform due to a impact and fixedly supports a sensor in the mountinghole formed in the intermediate portion of the outer race in its axialdirection can be realized.

By the bearing unit with the rotation speed detection instrument toachieve the second object, which comprises the outer race formed asdescribed above, a wheel is rotatably supported on the suspensiondevice, and an operation when the rotation speed of the wheel isdetected is the same as that of the well known conventional bearing unitwith the rotation speed detection instrument.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings, in which;

FIG. 1 is a sectional view showing a first embodiment of the presentinvention;

FIG. 2 is a sectional view of an outer race extracted from the sectionalview of FIG. 1;

FIG. 3 is an enlarged sectional view of the portion A of FIG. 2;

FIG. 4 is a sectional view showing a second embodiment of the presentinvention;

FIG. 5 is a sectional view showing of an outer race extracted from thesectional view of FIG. 4;

FIG. 6 is a sectional view taken along the line B—B of FIG. 5;

FIG. 7 is a sectional view showing a state in which a hardening coil isprovided on the inner side of the outer race;

FIG. 8 is a sectional view showing a third embodiment of the presentinvention, which is drawn similarly to FIG. 6;

FIG. 9 is a sectional view of an outer race, which shows a fourthembodiment of the present invention;

FIG. 10 is a sectional view taken along the line C—C of FIG. 9;

FIG. 11 is a fifth embodiment of the present invention;

FIG. 12 is a sectional view of an outer race extracted from thesectional view of FIG. 11;

FIG. 13 shows a sixth embodiment of the present invention, which is asectional view of an outer race before a hardened layer is formed;

FIG. 14 is a sectional view showing a situation in which the hardenedlayer is formed in the outer race;

FIG. 15 is a sectional view of the outer race in which the hardenedlayer and a sensor mounting hole are formed;

FIG. 16 shows a seventh embodiment of the present invention, which is asectional view of the portion A of FIG. 14;

FIG. 17 shows an eighth embodiment of the present invention, which is asectional view of an outer race before a hardened layer is formed;

FIG. 18 is a sectional view showing a situation in which the hardenedlayer is formed in the outer race;

FIG. 19 is a sectional view of the outer race in which the hardenedlayer is formed;

FIG. 20 is a sectional view showing another example of a plug, which isdrawn similarly to FIG. 18; and

FIG. 21 shows a ninth embodiment of the present invention, which is asectional view of an outer race.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1, 2 and 3 show a first embodiment of the present invention. Arolling bearing unit with a rotation speed detection instrument of thisembodiment comprises a hub 3 composed of a hub body 1 and an inner race2; an outer race 4; and a plurality of rolling elements 5 and 5. Aflange 6 for supporting a wheel is provided in an external side endportion of an outer peripheral surface of the hub body 1. Hereupon, theword “external” means the outside in the width direction of a car whenthe rolling bearing unit is assembled to the car and the left side ofFIGS. 1 and 2. On the contrary, the word “internal” means the inside ofthe car in its width direction and the right direction of FIGS. 1 and 2.Furthermore, an inner race track 7 is formed on the intermediate portionof the outer peripheral surface of the hub body 1. Besides the formationof the inner race track 7 directly on the intermediate of the outerperipheral surface of the hub body 1, the inner race track 7 issometimes formed on an outer peripheral surface of another inner racewhich is fitted on the intermediate of the outer peripheral surface ofthe hub body 1.

In an internal end portion of the outer peripheral surface of the hubbody 1, provided is a step portion 8 concentrically with the hub body 1,which formed by cutting the whole of the internal side end portion ofthe outer peripheral surface of the hub body 1 into its diameterdirection. The inner race 2 formed with another inner race track 7 inits outer peripheral surface is interference-fitted on and fixed to thestep portion 8. An internal end portion of the inner race 2 protrudesfrom the internal side end portion of the hub body 1 inward in a statewhere the inner race 2 is fitted on and fixed to the step portion 8. Theinternal side end portion of the inner race 8 is in contact with thestepped surface of a constant velocity joint (not shown) in a statewhere the rolling bearing unit is assembled in the car. Furthermore,also in a state where it is assembled in the car, a spline shaft annexedto the constant velocity joint is made to pass through a spline hole 9provided in the central portion of the hub body 1. A nut (not shown) isscrew-fitted on a male screw portion which is provided at a tip endportion of the spline shaft which protrudes from the external sideportion of the hub body 1, and is tightened. Upon this tightening of thenut, the step difference surface of the constant velocity joint stronglypresses the internal side end surface of the inner race 2, resulting inpreventing the inner race 2 from detaching from the step portion 8.Furthermore, a fitting portion 10 having a diameter slightly smallerthan that of the intermediate of the hub body 1 is provided in an endportion of the intermediate of the hub body close to the step portion 8.The diameter of the intermediate of the hub body 1 is larger than thatof the step portion 8. The outer diameter of the fitting portion 10 ismade slightly larger than the inner diameter of a later describedencoder 11 at the time when the encoder 11 is in a free state, so thatthe encoder 11 is interference-fitted on and fixed to the fittingportion 10. The outer diameter of the encoder 11 in the state where theencoder is fitted on the mounting portion 10, is made smaller than thatof a part of the intermediate of the hub body 1, which part ispositioned closer to the external side end portion than the fittingportion 10.

In the inner peripheral surface of the outer race 4, a plurality ofouter race tracks 12 and 12 are formed, which face the correspondinginner race tracks 7 and 7, respectively. A plurality of rolling elements5 and 5 are provided between the inner races 7, 7 and the outer racetrack 12, 12 with held by the retainers 13, 13, whereby the hub 3 isrotatably supported in the inside of the outer race 4. In theillustrated embodiment, though balls are used as the rolling elements 5and 5, tapered rollers can be used as the rolling elements, in the caseof the rolling bearing unit for use in cars which are heavy in weight.Moreover, in the outer peripheral surface of the outer race closer tothe internal end portion, provided is an attaching portion 14 forattaching the outer race 4 to the suspension device, which looks like aflange tending outward. Gaps between opening portions of the both endsof the outer race 4 and the intermediate of the outer peripheralsurface, and the inner end portion of the outer peripheral surface ofthe inner race 2 are closed by the sealing rings 15 and 15,respectively.

The encoder 11 is fitted on and fixed to the fitting portion 10 at theintermediate of the outer peripheral surface of the hub body 1,concentrically with the hub body 1. The encoder 11 is formed of amagnetic metal plate such as a steel plate, and is formed to becylindrical in its entirety. The encoder 11 is interference-fitted onand fixed to the fitting portion 10. The encoder 11 is arranged betweenthe lines of the rolling elements 5 and 5 provided in plural lines. Aplurality of through holes 16 and 16 are formed in the intermediate ofthe encoder 11 in its axial direction at equal intervals in itscircumference direction, whereby a magnetic characteristic of the outerperipheral surface of the encoder 11 is changed alternately in itscircumference direction and at equal intervals.

On the other hand, a mounting hole 17 is formed through in theintermediate of the outer race 4 in its axis direction and in theoutside position of the encoder 11 in its diameter direction, in a statewhere the inner peripheral surface of the outer race 4 and the outerperipheral surface of the outer race 4 are communicated to each other.Then, a sensor 18 including a detection device embedded in synthesisresin is inserted and fixed in the mounting hole 17, so that thedetection portion provided in the tip end surface of the sensor 18(drawn in the lowermost surface of FIG. 1) is allowed to face the outerperipheral surface of the encoder 11 with a small gap. In a state wherethe sensor 18 is inserted and fixed in the mounting hole 17, the sensor18 can detect the rotation speed of the encoder 11.

Furthermore, a flat attaching plane 19 is formed around the opening ofthe outer end of the mounting hole 17 and at the outer peripheralsurface of the outer race 4, which plane exists in a directionperpendicular to the central axis of the mounting hole 17. A conicalconcave chamfered portion 20 and a cylindrical receiving plane 21 areformed in the connection portion between the attaching plane 19 and theinner peripheral surface of the mounting hole 17, in this order. On theother hand, an attaching portion 22 is fixedly provided in the base endportion of the sensor 18 (drawn in the uppermost end portion of FIG. 1),and the attaching portion 22 is connected to the outer race 4 to fix toeach other, by a screw (not shown) which is made to pass through the endportion of the attaching portion 22. In this situation, an O-ring 23fitted on the base end portion of the sensor 18 is elasticallycompressed between the outer peripheral surface of its base end portionand the inner peripheral surface of the receiving plane 21, whereby theportion attaching the sensor 18 is sealed and it is prevented that anextraneous material such as rain invades inside of the inner race 4through the mounting hole 17.

Furthermore, hardened layers 24 and 24 having a hardness of 500 Hv ormore are formed in the inner peripheral surface of the outer race 4, andin the portions where the respective outer race tracks 12 and 12 areformed. The hardened layers 24 and 24 serve to secure a rolling fatiguelife time of the portions of the outer race where outer race tracks 12,12 are formed, regardless of loads repeatedly applied from the rollingsurfaces of the rolling elements 5 and 5 to the tracks, and have athickness of 1.5 mm or more, as described. Particularly, the rollingbearing unit with the rotation speed detection instrument of thisembodiment is applied to the one in which the distance L (see FIG. 3)between the mounting hole 17 and the end periphery of the outer racetrack 12 which is positioned closer to the mounting hole 17, of theouter race tracks 12 and 12 that is, which is located on the right sideof FIGS. 1 and 2, ranges from 2 to 10.5 mm. In addition, in the case ofthis embodiment, in order to keep the minimum distance between themounting hole 17 and the hardened layer 24, 24 formed in each of theportions where the outer race tracks 12, 12 are formed at 0.5 mm ormore, the thickness T of each of the hardened layers 24 and 24 (see FIG.3) is regulated so that the portion constituting the mounting hole 17 isleft to be raw steel material which is not hardened or semi-raw steelmaterial which is soft.

In the case where the distance L is less than 2 mm, it is impossible tosecure the rolling fatigue life time of the outer race tracks 12 and 12and to make the working of the mounting hole 17 easy. Furthermore, inthe case where the distance L exceeds 10.5 mm, the working of themounting hole 17 can be easily performed without regulating thethickness T of the hardened layers 24 and 24. In other words, in acomparatively large-sized bearing unit with a rotation speed detectioninstrument in which the distance L exceeds 10.5 mm, the working of themounting hole 17 can be easily performed. However, in the case of arolling bearing unit in which the distance L is 10.5 mm or less, if theregulation of the thickness T of the hardened layers 24 and 24 is notperformed, the working of the mounting hole 17 becomes troublesome.Specifically, this embodiment is applied to a comparatively small-sizedrolling bearing unit with a rotation speed detection instrument in whichthe distance L does not exceed 10.5 mm.

In the case of the rotation bearing unit with a rotation speed detectioninstrument of this embodiment, the wheel fixed to the flange 6 which isprovided in the external side end portion of the hub body 1 can berotatably supported on the suspension device supporting the outer race4. Furthermore, when the encoder 11 fixedly fitted on the inner race 2rotates with the rotation of the wheel, the through holes 16 and 16formed in the intermediate of the encoder 11 in its axial direction andthe pole portions each existing between the through holes 16 and 16which are adjacent to each other in the circumference direction,alternately pass through near the detection portion provided in the tipend surface of the sensor 18. As a result, a density of magnetic fluxflowing through the sensor 18 changes, and an output of the sensorchanges. The frequency in which the output of the sensor 18 changes isproportional to the rotation speed of the wheel. Therefore, if theoutput of the sensor is sent to a controller (not shown), the ABS andthe TCS can be suitably controlled.

Particularly, in the case of the rolling bearing unit with a rotationspeed detection instrument of this embodiment, the working of themounting hole 17 for supporting the sensor 18 on the outer race 4 can beeasily performed without making the hardening treatment for the hardenedlayers 24 and 24 troublesome, which layers are formed at the portions ofthe outer race where the tracks 12 and 12 are formed. Specifically,since the distance L between the mounting hole 17 and the end peripheryof the outer race track 12, which is located on the right side of FIGS.1 and 2 and closest to the mounting hole 17 among the outer race tracks12 and 12, is set to be 2 mm or more, the minimum thickness (1.5 mm) ofthe hardened layer 24, which is required for securing the durability ofthe outer race track 12, can be secured. As a matter of course, theminimum thickness (1.5 mm) of the hardened layer 24, which is requiredfor securing the durability of the outer race 12, can be secured for theouter race track 12 which is farther from the mounting hole 17, that is,on the left side of FIGS. 1 and 2. The minimum distance between themounting hole 17 and the hardened layers 24 and 24 formed at theportions of the outer race where the tracks 12 and 12 are formed, is setto 0.5 mm or more, so that the mounting hole 17 can be formed at aportion which is apart from the transition layer, and is raw and soft,and the working of the mounting hole 17 can be easily performed evenafter the formation of the hardened layers 24 and 24 in the portions ofthe outer race where the tracks 12 and 12 are formed. It should be notedthat the control of the thickness of the hardened layers 24 and 24 canbe comparatively easily performed by regulating the amount of the powersupply to the hardening coil and the power supply time thereto.

Next, FIGS. 4, 5 and 6 show a second embodiment of a roiling bearingunit with a rotation speed detection instrument of the presentinvention. In the case of this embodiment, the hardened layers 24 and 24respectively provided in the inner peripheral surface of the outer race4 and in the portions of the outer race where the tracks 12 and 12 areformed, are connected by the jointing hardened layer 25 provided at aposition apart from the mounting hole 17 in a circumference direction ofthe outer race 4. In other words, the outer race tracks 12 and 12 In theinner peripheral surface of the outer race 4 and the portion between theouter race tracks 12 and 12 except the peripheral portion of themounting hole 17 are made to be harder than the hardness of 500 Hv bythe hardened layers 24 and 24 and the jointing hardened layer 25. In thecase of this embodiment, the minimum distance between each hardenedlayer 24, 24 and the mounting hole 17 is not only set to 0.5 mm or more,the minimum distance L′ (see FIG. 6) between the jointing hardened layer25 and the mounting hole 17 is but also set to 0.5 mm or more. Thus, theportion of the mounting hole 17 is made to be raw steel material whichis not hardened or to be semi-raw steel material which is soft.

In the case of this embodiment constructed as described above, theportion which is a part of the outer race 4 and between the outer racetracks 12 and 12, becomes less apt to deform plastically. For thisreason, even when upon crashing of the wheel against the paving stone animpact load is applied to the outer race 4 through the hub 3 and therolling elements 5 and 5, the outer race 4 is less apt to deformplastically, so that the durability of the rolling bearing unit with arotation speed detection instrument including the wheel 4 can beenhanced. Also in the case of this embodiment, the raw steel materialportion which is not hardened is left around the jointing hardened layer25 and the toughness of the outer race 4 is secured, so that occurrenceof the damages such as cracks in the outer race 4, due to the foregoingimpact load, is prevented.

It should be noted that in order to form the hardened layers 24 and 24and the jointing hardened layer 25 as described in this embodiment, thehardening coil 26 in which its portion facing the opening portion of themounting hole 17 on its inner diameter side is concaved inward in itsdiameter direction is used. Specifically, the outer peripheral surfaceof the hardening coil 26 has a shape almost according the innerperipheral surface shape of the outer race 4, and a concave portion 27is formed at its portion facing the opening portion of the mounting hole17 on its inner diameter side. In the situation where such hardeningcoil 16 is disposed inside the outer race 4 concentrically with theouter race 4, when an electric current is blown through the coil 26, theplural outer race tracks 12 and 12 and the portion between the outerrace tracks 12 and 12 are heated except the peripheral portion of themounting hole 17, and this heated portion can be treated by hardening.It should be note that when only the predetermined portion in the innerperipheral surface of the outer race 4 is hardened using the hardeningcoil 26 as described above, in order to strictly define the boundarybetween the portion which is to be hardened and the portion which is notto be hardened, it is conceived to shorten the distance between theouter peripheral surface of the hardening coil 26 and the innerperipheral surface of the outer race 4. In such case, when the outerdiameters of the convex portions existing in both end portions of thehardening coil 26 in its axis direction becomes larger than the innerdiameter of the minimum diameter portion existing in the intermediate ofthe outer race 4 in its axis direction, the hardening coil 26 isconstructed so that it can be split into two pieces in its axisdirection. It should be noted that in the case of this embodiment,although the distance between the mounting hole 17 and the end peripheryof the outer race track 12 closer to the mounting hole 17 needs not tobe 10.5 mm or less, it may be at a range from 2 to 10.5 mm as a matterof course. The constitution and operation of the rolling bearing unit ofthis embodiment are the same as those of the first embodiment.

As another method to achieve the structure of the second embodiment ofthe present invention shown in FIGS. 4, 5 and 6, the hardened layers 24and 24 located in the portions of the outer race where the outer racetracks 12 and 12 are formed and the jointing hardened layer 25 can bealso formed sequentially. For example, it is conceived that after thejointing hardened layer 25 is formed in the state the outer race 4 is ata standstill, the hardened layers 24 and 24 are formed while rotatingthe outer race 4, and then the hardened layers 24 and 24 and thejointing hardened layer 25 are connected. Alternatively, it is alsopossible that after the hardened layers 24 and 24 are formed, thejointing hardened layer 25 is formed to connect the hardened layers 24and 24.

FIG. 8 shows an outer race of a third embodiment of the presentinvention. Since the structure of an inner race of the third embodimentis the same as that of the second embodiment, an illustration anddescription for it are omitted. In the second embodiment, the jointinghardened layer 25 for connecting the hardened layers 24 and 24 with eachother, provided at the portions where the outer race tracks 12 and 12are formed, is provided almost in its all circumference except for theportion of the mounting hole 17. In the case of this third embodiment,the jointing hardened layers 25 are intermittently formed at threeportions in the circumference direction. The mounting hole 17 isdisposed between the jointing hardened layers 25 and 25 adjacent to eachother in the circumference direction. A structure, operation andmanufacturing method of the roiling bearing unit of the presentembodiment are the same as those of the first embodiment.

FIGS. 9 and 10 show an outer race of a fourth embodiment of the presentinvention. Since the structure of an inner race of the third embodimentis the same as that of the first or second embodiment, an illustrationand description for it are omitted. In the case of this fourthembodiment, the jointing hardened layers 25 are intermittently formed attwo portions in the circumference direction of the inner peripheralsurface of the outer race 4. The mounting hole 17 is disposed betweenthe jointing hardened layers 25 and 25 adjacent to each other in thecircumference direction. A structure, operation and manufacturing methodof the rolling bearing unit of the present fourth embodiment are thesame as those of the first embodiment.

Since the rolling bearing unit of the foregoing embodiment of thepresent invention is constituted as described above and operates, adecrease in cost of the rolling bearing unit with a rotation speeddetection instrument can be achieved by making the working operation ofthe bearing unit easy. Furthermore, according to demand, the foregoingembodiment can also cope with a reduction in a size and a weight of thebearing unit.

FIGS. 11 and 12 show a fifth embodiment of the present invention. Therolling bearing unit with a rotation speed detection instrument of thisfifth embodiment comprises a hub 3 composed of a hub body 1 and an innerrace 2; an outer race 4; and a plurality of rolling elements 5 and 5. Aflange 6 for supporting a wheel is provided in an external side endportion of an outer peripheral surface of the hub body 1. Hereupon, theword “external” means the outside in the width direction of a car whenthe rolling bearing unit is assembled to the car and the left side ofFIGS. 11 and 12. On the contrary, the word “internal” means the insideof the car in its width direction and the right direction of FIGS. 11and 12. Furthermore, an inner race track 7 is formed on the intermediateportion of the outer peripheral surface of the hub body 1. Besides theformation of the inner race track 7 directly on the intermediate of theouter peripheral surface of the hub body 1, the inner race track 7 issometimes formed on an outer peripheral surface of another inner racewhich is fitted on the intermediate of the outer peripheral surface ofthe hub body 1.

In an internal side end portion of the outer peripheral surface of thehub body 1, provided is a step portion 8 concentrically with the hubbody 1, which formed by cutting the whole of the internal side endportion of the outer peripheral surface of the hub body 1 into itsdiameter direction. The inner race 2 formed with another inner racetrack 7 in its outer peripheral surface is interference-fitted on andfixed to the step portion 8. An internal side end portion of the innerrace 2 protrudes from the internal side end portion of the hub body 1inward in a situation where the inner race 2 is fitted on and fixed tothe step portion 8. The internal side end portion of the inner race 8 isin contact with the stepped surface of a constant velocity joint (notshown) in a state where the rolling bearing unit is assembled in thecar. Furthermore, also in a situation where it is assembled in the car,a spline shaft annexed to the constant velocity joint is made to passthrough a spline hole 9 provided in the central portion of the hub body1. A nut (not shown) is screw-fitted on a male screw portion which isprovided at a tip end portion of the spline shaft which protrudes fromthe external side portion of the hub body 1, and is tightened. Upon thistightening of the nut, the stepped surface of the constant velocityjoint strongly presses the internal side end surface of the inner race2, resulting in preventing the inner race 2 from detaching from the stepportion 8. Furthermore, a fitting portion 10 having a diameter slightlysmaller than that of the intermediate of the hub body 1 is provided inan end portion of the intermediate of the hub body close to the stepportion 8. The diameter of the intermediate of the hub body 1 is largerthan that of the step portion 8. The outer diameter of the fittingportion 10 is made slightly larger than the inner diameter of a laterdescribed encoder 11 at the time when the encoder 11 is in a free state,so that the encoder 11 is interference-fitted on and fixed to thefitting portion 10. The outer diameter of the encoder 11 is made smallerthan that of a part of the intermediate of the hub body 1, which part ispositioned closer to the external side end portion than the fittingportion 10.

In the inner peripheral surface of the outer race 4, a plurality ofouter race tracks 12 and 12 are formed, which face the correspondinginner race tracks 7 and 7, respectively. A plurality of rolling elements5 and 5 are provided between the inner races 7, 7 and the outer racetrack 12, 12 with held by the retainers 13, 13, whereby the hub body 1and the inner race 2 are is rotatably supported in the inside of theouter race 4. In the illustrated embodiment, though balls are used asthe rolling elements 5 and 5, tapered rollers can be used as the rollingelements, in the case of the rolling bearing unit for use in cars whichare heavy in weight. Moreover, in the outer peripheral surface of theouter race closer to the internal side end portion, provided is anoutwardly extending flange-like attaching portion 14 for attaching theouter race 4 to the suspension device. Gaps between opening portions ofthe both ends of the outer race 4 and the intermediate of the outerperipheral surface, and the inner end portion of the outer peripheralsurface of the inner race 2 are closed by the sealing rings 15 and 15,respectively.

The encoder 11 is fitted on and fixed to the fitting portion 10 at theintermediate of the outer peripheral surface of the hub body 1,concentrically with the hub body 1. The encoder 11 is formed of amagnetic metal plate such as a steel plate, and is formed to becylindrical in its entirety. The encoder 11 is interference-fitted onand fixed to the fitting portion 10. The encoder 11 is arranged betweenthe lines of the rolling elements 5 and 5 provided in plural lines. Aplurality of through holes 16 and 16 are formed in the intermediate ofthe encoder 11 in its axial direction at equal intervals in itscircumferencial direction, whereby a magnetic characteristic of theouter peripheral surface of the encoder 11 is changed alternately in itscircumferencial direction at equal intervals.

On the other hand, a mounting hole 17 is formed through in theintermediate of the outer race 4 in its axial direction and in theoutside position of the encoder 11 in its diameter direction, in a statewhere the inner peripheral surface of the outer race 4 and the outerperipheral surface of the outer race 4 are communicated to each other.Then, a sensor 18 including a detection device embedded in synthesisresin is inserted and fixed in the mounting hole 17, so that thedetection portion provided in the tip end surface of the sensor 18(drawn in the lowermost surface of FIG. 11) is allowed to face the outerperipheral surface of the encoder 11 with a small gap. In a state wherethe sensor 18 is inserted and fixed in the mounting hole 17, the sensor18 can detect the rotation speed of the encoder 11.

Furthermore, a flat attaching plane 19 is formed around the opening ofthe outer end of the mounting hole 17 and at the outer peripheralsurface of the outer race 4, which plane exists in a directionperpendicular to the central axis of the mounting hole 17. A conicalconcave chamfered portion 20 and a cylindrical receiving plane 21 areformed in the connection portion between the attaching plane 19 and theinner peripheral surface of the mounting hole 17, in this order. On theother hand, an attaching portion 22 is fixedly provided in the base endportion of the sensor 18 (drawn in the uppermost end portion of FIG. 1),and the attaching portion 22 is connected to the outer race 4 to fix toeach other, by a screw (not shown) which is made to pass through the endportion of the attaching portion 22. In this situation, an O-ring 23fitted on the base end portion of the sensor 18 is elasticallycompressed between the outer peripheral surface of its base end portionand the inner peripheral surface of the receiving plane 21, whereby theportion attaching the sensor 18 is sealed and it is prevented that anextraneous material such as rain invades inside of the inner race 4through the mounting hole 17.

Moreover, the hardened layer 24 exhibiting a hardness of, for example,500 Hv or more is formed in the portions of the outer race 4 where theouter race tracks 12, 12 are formed and the portion between the outerrace tracks 12 and 12 on the inner peripheral surface of the outer race4. The portions of the hardened layer 24 existing on the outer racetracks 12 and 12 secure the rolling fatigue life time of the outer racetracks 12 and 12 regardless of loads repeatedly applied thereto from therolling surfaces of the rolling elements 5 and 5. Contrary to this, bymaking the intermediate of the hardened layer 24 located between theouter race tracks 12 and 12 less apt to deform plastically, it can beprevented that the portion of the outer race 4 located between the outerrace tracks 12 and 12 deforms plastically, regardless of an impact loadapplied from the rolling elements 5 and 5 due to running of the wheel onthe paving stone.

The hardened layer 24 is formed by heating the outer race 4 from itsinner peripheral surface side while cooling the outer peripheral surfaceof the outer race 4 with coolant such as cooling water and cooling oil.It should be noted that a hardened layer of sixth embodiment describedlater is formed in the same manner as this embodiment. The reason whythe hardened layer 24 is formed while cooling the outer peripheralsurface of the outer race 4 is that by preventing a production of anextremely large outer diameter of the hardened layer 24 and preventing aproduction of an hardened outer peripheral surface of the outer race 4,toughness of the outer race 4 is secured, and an occurrence of damagessuch as cracks of the outer ring 4 is prevented regardless of an impactload which may be applied during running of cars. In addition, by makingsmall the thickness of the hardened layer 24 in which the working of themounting hole 17 is difficult, the working of the mounting hole 17 ismade easy.

The mounting hole 17 is formed in the intermediate of the outer race 4in its axial direction between the outer race tracks 12 and 12. Themounting hole 17 is formed by a drill with a super-hard drill or aceramic chip after the hardened layer 24 is formed. Noted that thehardened layer 24 is previously formed on the inner peripheral surfaceof the outer race 4. Although the portion of the hardened layer 24existing closer to the inner peripheral surface exhibits a hardness of,for example, 500 Hv or more, the drill comprising the super-hard drillor the ceramic chip is enough to form the fitting hole 17. Therefore,the mounting hole 17 for fixedly supporting the sensor 18 can be formedin the outer race 4 in which its deformation is prevented by thehardened layer 24. It should be noted that when the mounting hole 17 isformed by cutting with the drill provided the super-hard drill or theceramic chip, cooling and lubrication for the cut portion are performedby pouring cutting oil at least on the cutting portion. As the lubricantoil used at the cutting, nonaqueous oil is preferable. Since a heatgenerated at the time when the mounting hole 17 is formed in thehardened layer 24 is much, a working speed (rotation speed of the drill)should be slower compared to the case where a raw steel material isworked for forming a hole therein, in addition to pouring the cuttingoil. Specifically, the cutting speed for making the mounting hole 17 bythe drill is 20 m/min or less expressed by a speed at an outerperipheral surface of the drill, preferably 10 m/min or less, when theinner diameter of the mounting hole 17, that is, the outer diameter ofthe drill, is set to a range from about 11 to 13 mm. It should be notedthat a cutting speed when the mounting hole 17 is formed in the rawsteel material but not in the hardened layer is about at a range fromabout 35 to 41 m/min.

In the case of the rolling bearing unit with a rotation speed detectioninstrument of the present invention as described above, the wheel fixedto the flange 6 which is provided in the outer end portion of the hubbody 1 can be rotatably supported on the suspension device which supportthe outer race 4. Furthermore, when with the rotation of the wheel theencoder 11 fixedly fitted on the inner race 2 rotates, the through holes16 and 16 provided in the intermediate of the encoder 11 in its axialdirection and the pole portions existing between the through holes 16and 16 alternately pass through the vicinity of the detection portionprovided in the tip surface of the sensor 18. As a result, the amount ofthe magnetic flux (density) flowing through the sensor 18 changes andthe output of the sensor 18 changes. The frequency in which the outputof the sensor 18 changes as described above is proportional to therotation speed of the wheel. Therefore, if the output of the sensor 18is sent to a controller (not show), the ABS and the TCS can be suitablycontrolled.

FIGS. 13, 14 and 15 show an outer race of a sixth embodiment of thepresent invention. An inner race of this embodiment is the same as thatof the fifth embodiment, and an illustration for it is omitted. In thecase of this embodiment, the hardened layer 24 located at the portionsof the outer race where the outer race tracks 12 and 12 are located andthe portion located between the inner race tracks 12 and 12, is formedin a state where a concaved hole 2 having a bottom which hole is anorigin of the mounting hole 17 has been formed from the outer peripheralsurface side of the intermediate of the outer race 4. The mounting hole17 is perforated thourhg to the inner peripheral surface side of theouter race 4 after the formation of the hardened layer 24.

As shown in FIG, 13, the concaved hole 27 with the bottom which is theorigin of the mounting hole 17 is formed from the outer peripheralsurface side of the outer race 4 to the mid way in its diameterdirection, and then the outer race 4 is heated from its inner peripheralsurface side while cooling the outer peripheral surface side thereof bycooling the outer race 4 with coolant such as cooling water or coolingoil, as shown in FIG. 14. Thus, as shown in FIG. 14, the hardened layer24 is formed, which has an intermediate portion having a smaller outerdiameter than other portions. Thereafter, the bottom portion of theconcaved hole 27 is scraped off by a drill comprising a super-hard drillor a ceramic chip, and the mounting hole 17 which is perforated throughthe outer peripheral surface side to the inner peripheral surface sideof the outer race 4 is formed as shown in FIG. 15. The working for thebottom portion of the concaved hole 27 must be performed using a hardtool such as a drill comprising a super-hard drill or a ceramic chip.Noted that since a working cost is low in the case of this embodiment,the working operation is easy to be performed. Furthermore, sincenecessity for working both of the raw steel material and the hardenedportion with the same tool is less, the working with a high efficiencycan be performed while preventing a clog in the tool.

As described above, in order to avoid the working of the raw steelmaterial and the hardened portion with the same tool as possible, therelation between the thickness of the hardened layer 24 and the depth ofthe concaved portion 27 should be preferably regulated so that thehardened layer 24 reaches the bottom portion of the concaved hole 27.Furthermore, in order to suppress the deformation of the vicinity of thebottom portion of the concaved hole 27 as little as possible at the timeof the heat treatment to form the hardened layer 24, the thickness ofthis bottom portion, that is, the distance from the bottom surface ofthe concaved hole 27 to inner peripheral surface of the outer race 4,should be secured to 1 mm or more. In the case of this embodiment, whenthe hardened layer 24 is formed as described above, the outer peripheralsurface of the outer race 4 is cooled by coolant. However, this coolantnever passes through the mounting hole 17 to reach the inner peripheralsurface of the outer race 4. For this reason, it is prevented that thecoolant adheres to the portion on the inner peripheral surface of theouter race 4, in which the hardened layer 24 is to be formed, therebycausing unevenness of the hardened layer 24.

FIG. 16 shows a part of the outer race of a seventh embodiment of thepresent invention. The inner race of this embodiment is the samestructure as that of the fifth embodiment, and an illustration anddescription for it are omitted. In the case of this seventh embodiment,the concaved hole 27 a formed in the position, which is located in theintermediate portion of the outer race 4 in its axial direction andbetween the outer race tracks 12 and 12 (see FIGS. 11 to 15), has astructure so that its portion closer to the inner peripheral surface isdeeper than its other portion. In the case of this seventh embodiment,the hardened layer is formed at a predetermined portion on the innerperipheral surface of the outer race 4 while cooling the outer peripherysurface of the outer race 4 by coolant such as cooling water or coolingoil in a situation where the concaved hole 27 a has been formed.Thereafter, the bottom portion 28 of the concaved hole 27 a is punchedout by a punch (not shown) in a situation where the inner peripheralsurface of the outer race 4 tightly contacts a counter punch (notshown), and the mounting hole which reaches from the outer peripheralsurface of the outer race 4 to the inner peripheral surface thereof isformed. It should be noted that the punch working for the bottom portionof the mounting hole can be made easier by making the inner diameter ofthe inner end of the mounting hole to be punched off as small aspossible, according to the outer diameter of the tip end of the sensor.

FIGS. 17 to 20 show an outer race of an eighth embodiment of the presentinvention. An inner race of this embodiment is the same as that of thefifth embodiment, and an illustration and description for it areomitted. In the case of this embodiment, after the mounting hole 17 hasbeen formed between the inner race tracks 12 and 12, the hardened layer24 located in the portions where the outer race tracks 12 and 12 areformed and between the outer race tracks 12 and 12 in the innerperipheral surface of the outer race, 4 is formed in a state where theouter end opening of the mounting hole 17, that is, the opening on theouter peripheral surface side of the outer race 4, is hermeticallysealed or substantially sealed by a plug 25. The hardened layer 24 isformed while cooling the outer peripheral surface of the outer race 4 bycoolant such as cooling water or cooling oil.

Specifically, to form the hardened layer 24 and the mounting hole 17 inthe outer race 4, the mounting hole 17 is formed between the outer racetracks 12 and 12 and in the intermediate portion of the outer race 4 inits axial direction in a state where a hardened layer has not yet beenformed on the outer race 4 and the outer race 4 remains raw, as shown inFIG. 17. Thereafter, an electric current is flown through a heating coil(not shown) disposed inside the outer race 4 while cooling theintermediate portion of the outer peripheral surface of the outer race 4including the vicinity of the mounting hole 17 by coolant, in a statewhere the mounting hole 17 is hermetically sealed or substantiallysealed by a plug 25 formed of a heat resistant material such metals andceramics, as shown in FIG. 18 whereby the inner peripheral surface ofthe outer race 4 is heated, and the hardened layer 24 is formed.Thereafter, by detaching the plug 25, the outer race 4 as illustrated inFIG. 19 is obtained. It should be noted that the O-ring 26 (see FIG. 18)is provided between the base portion of the plug 25 and the seat surface21 formed in the mounting hole 17, and this disables the coolant toenter between the outer peripheral surface of the plug 25 and the innerperipheral surface of the mounting hole 17.

Furthermore, when the plug 25 is formed of elastomer such as rubber orelastic: material such as synthesis resin, the mounting hole 17 can behermetically sealed based on elasticity of the plug 25. In such cases,as shown in FIG. 20, the dimension of the plug in its axial directionmay be set to be small. Furthermore, the plug may be a plate formed ofmetal or synthesis resin, which does not enter the mounting hole 17,that is, the plate is larger than the mounting hole 17. Alternatively,the plug may be so shaped, that a part of the plug is loosely fit in orenter the mounting hole 17. In this case, the plate-shaped plug may bepressed against the mounting hole 17 from the outer periphery surface ofthe outer race 4 by a coil or a band separately provided from the plug,thus sealing the mounting hole 17. As described above, when thedimension of the plug 25 in its axial direction is set to be small, itcan be prevented that a portion of the inner peripheral surface of themounting hole 17 which portion contacts the heating coil is heated to ahigh temperature when an electric current is flown throug to the heatingcoil. Therefore, even when the plug 25 is not formed of a heat-resistantmaterial, the plug 25 is never damaged at the time of the innerperipheral surface of the outer race 4.

It should be noted that an O-ring 26 has a function to allow the plug 25to be easily detachable in the mounting hole 17, while enabling the plug25 to be temporarily tacked in the mounting hole 17. Furthermore, whenthe inner peripheral surface of the outer race 4 may be heated, the endopenings of the outer race 4 may be also sealed by sealing plates (notshown) and the like, to prevent entering of the coolant inside the outerrace 4. For such sealing plates, it is prevented that the coolant isattached to the portion located on the inner peripheral surface of theouter race 4, where the hardened layer 24 is to be formed, therebycausing unevenness in the hardened layer 24. In the case of thisembodiment as described above, since the mounting hole 17 is formed inthe foregoing intermediate portion in a state where the intermediateportion where the hardened layer 24 is not formed yet remains raw fromthe outer peripheral surface to the inner peripheral surface, theworking of the mounting hole 17 can be easily performed.

FIG. 21 shows a ninth embodiment of the present invention. In the caseof this embodiment, the mounting hole 17 is formed in the intermediateportion of the outer race 4 in its axial direction and in the portionbetween the outer race tracks 12 and 12, before the hardened layer isformed in the inner peripheral surface of the outer race 4. Thereafter,while rotating the outer race 4, the outer peripheral surface of theouter race 4 is cooled by liquefied coolant which is blown up as shownby the arrow of FIG. 21 upward, and at the same time the innerperipheral surface of the outer race 4 is heated, thereby forming thehardened layer. The strength of blowing-up of the liquefied coolantshown by the arrow of FIG. 21 is set to a value so that the coolant doesnot enter the outer race 4 through the mounting hole 17 even when themounting hole 17 tends downward as shown in FIG. 21. Specifically, thestrength of the blowing-up of the coolant is a value that though thecoolant reaches the outer peripheral surface of the outer race 4 (lowersurface), the coolant does riot reach the inner peripheral surface ofthe outer race 4. Also in the case of this embodiment, in a state theforegoing intermediate portion remains raw from the outer peripheralsurface to the inner peripheral surface, in which the hardened layer isnot formed, the mounting hole 17 is formed in this intermediate portion,so that the working of the mounting hole 17 can be easily performed.

Furthermore, after the mounting hole is formed in the outer race, if theformation operation of the hardened layer is performed while cooling theouter peripheral surface of the outer race using gaseous coolant, theformation operation of the hardened layer can be performed withoutsealing the mounting hole with a plug or regulating the strength ofblowing the coolant. As the gaseous coolant used in this case, lowtemperature nitrogen gas obtained by evaporating liquefied nitrogen canbe used. When such gaseous coolant is used, though the outer race needsnot to be rotated. When the outer race is not rotated, a plurality ofspraying nozzles are arranged around the outer race so that the gaseouscoolant is evenly sprayed on the outer peripheral surface of the outerrace.

The foregoing embodiments described above using the drawings concern thecase in which the present invention is applied to the rolling bearingunit for supporting driving wheels, that is, rear wheels of the FR carand the RR car, front wheels of the FF car and all wheels of the 4WDcar. The present invention can be applied also to a rolling bearing unitfor supporting driven wheels, that is, rear wheels of the FR car and theRR car, and rear wheels of the FF car. Furthermore, the presentinvention has a feature in that the formation operation of the mountinghole for fixedly supporting the sensor which is disposed in theintermediate portion of the outer race can be easily carried out. Thesorts of the rotation speed detection instrument including the sensorand the encoder are not particularly limited. Therefore, the rotationspeed detection instrument is not limited to the magnetic detection typesuch as the foregoing embodiments and other types such as eddy currenttype, photoelectric type can be adopted.

The rolling bearing unit of the present invention is constructed andoperates as described above, so that by facilitating the workingoperation of the outer race constituting the rolling bearing unit with arotation speed detection instrument, a reduction in cost of the rollingbearing unit with a rotation speed detection instrument can be achieved.

Although the preferred embodiments of the present invention have beendescribed in detail, it should be understood that various changes,substitutions and alternations can be made therein without departingfrom spirit and scope of the inventions as defined by the appendedclaims.

What is claimed is:
 1. A rolling bearing unit with a rotation speeddetection instrument comprising: a hub rotating together with a wheelduring use, the hub having a plurality of inner race tracks in an outerperipheral surface thereof; an outer race formed of steel material,which is supported by a suspension device and does not rotate duringuse, the outer race having a plurality of outer race tracks in an innerperipheral surface which face the inner race tracks; rolling elements,each being rotatably provided between a respective inner race track anda corresponding outer race track; an encoder fixedly provided at aportion of the outer peripheral surface of the hub between the innerrace tracks, the encoder exhibiting a characteristic which changes in acircumferential direction alternately at equal intervals; and a sensorhaving a detecting section, the sensor being supported in a mountinghole provided in an intermediate portion of the outer race in an axialdirection so that the detecting section may face the encoder and changean output signal in response to the change of the characteristic of theencoder, wherein a hardened layer is formed on the inner surface of theouter race and each portion where the outer race tracks are formed, anda distance between an end periphery of the outer race track which iscloser to said mounting hole and the mounting hole is 10.5 mm or less,and a portion where said mounting hole is formed is not hardened and athickness of the hardened layer formed in the outer race track closestto said mounting hole is 1.5 mm or more.
 2. A rolling bearing unit witha rotation speed detection instrument comprising: a hub rotatingtogether with a wheel during use, the hub having a plurality of innerrace tracks in an outer peripheral surface thereof; an outer race formedof steel material, which is supported by a suspension device and doesnot rotate during use, the outer race having a plurality of outer racetracks in an inner peripheral surface which face the inner race tracks;rolling elements, each being rotatably provided between a respectiveinner race track the and a corresponding outer race track; an encoderfixedly provided at a portion of the outer peripheral surface of the hubbetween the inner race tracks, the encoder exhibiting a characteristicwhich changes in a circumferential direction alternately at equalintervals; a sensor having a detecting section, the sensor beingsupported in a mounting hole provided in an intermediate portion of theouter race in an axial direction so that the detecting section faces theencoder and changes an output signal in response to the change of thecharacteristic of the encoder; and a hardened layer exhibiting ahardness of 500 Hv or more, being formed on the inner surface of theouter race and at each portion where the outer race tracks are formed,wherein a distance between the mounting hole and an end periphery of theouter race track closest to the mounting hole among said outer racetracks is at a range from 2 to 10.5 mm, and a minimum distance betweensaid mounting hole and the hardened layer is 0.5 mm.